A conventional glass syringe is being replaced with a resin syringe and, in a disposable syringe, a resin syringe is becoming more popular for hygienic and disposal reasons. In addition, prefilled syringe formulations are becoming prevalent in the medical field for the reason that, for example, prefilled syringe formulations eliminate the effort required in a conventional injection of pouring a drug from another container, such as a vial or an ampoule, into a syringe, and enable easier aseptic preparation. However, since a conventional resin container tends to be more oxygen permeable, unlike a glass bottle and a metallic container, the resin container still has a problem in terms of the storage stability of its content after filling and sealing the resin container and the replacement thereof with such resin containers has not actually made strong progress. Therefore, recently, there has been a need for replacement of glass syringes, which have been used for a long time, with resin syringes.
In general, when a syringe barrel is molded, a method of forming two gates in a flange or two gates in a body part is commonly used in order to secure the circularity of a cylindrical part. However, such molding method has a disadvantage in that welded parts are formed and the mechanical strength of the syringe barrel is lowered. On the other hand, if injection is performed from a nozzle part, mechanical strength can be secured without the formation of any welded part and circularity can also be secured. Further, if there is only one gate, the runner balance in a mold can be adjusted easily and the number of cavities per volume can be increased. However, if a syringe barrel is molded by performing injection from a nozzle part, a remaining gate at the nozzle part has to be cut by a certain method. As a known technique in a method of cutting a resin tube, a rotary blade or grinding wheel may be used. However, such method produces chips. Since a syringe barrel is produced in a clean room, the generation of chips in cutting the remaining gate at the nozzle part will require a dedicated booth or dust collector or require a cleaning apparatus for removing the chips inside the nozzle, which is not economical.
In order to solve this problem, a proposed manufacturing method includes the use of equipment having a structure in which, for example, in an extrusion manufacturing line of a synthetic resin tube, a force-cutting blade is rotated around the synthetic resin tube to cut the synthetic resin tube, while a press roll, which is provided separately from the force-cutting blade, is rotated around the synthetic resin tube so as to follow the force-cutting blade with the press roll being positioned on a cutting line of the tube, in order to suppress the generation of chips (see Patent document 1).
On the other hand, in a plastic bottle for foods and beverages in a technical field in which the replacement of glass with resin has made progress, the storage stability of content after filling and sealing the plastic bottle has been improved by co-extruding a preform including polyethylene terephthalate resin in a skin layer and a thermoplastic resin having a gas barrier property in a core layer and then performing blow molding. A molding method using such technique has been proposed, in which a polyolefin resin and a barrier resin are subjected to coinjection molding with a gate being located on a nozzle side of a barrel to produce a barrel having a multilayer structure having an innermost layer and an outermost layer formed of the polyolefin resin and a core layer formed of the barrier resin, and the molding is performed with an open nozzle of an injection unit being in close contact with a nozzle tip surface in order to avoid any remaining gate (Patent Document 2).